The invention relates to a plunger for a cold chamber type casting machine comprising a hollow shaft fastened at the plunger, a cooling liquid pipe arranged within the shaft with a radial interspace and projecting axially beyond the shaft and into a tube-like body arranged within the plunger forming an annular chamber between the tube-like body and the plunger casing, the annular chamber at both plunger ends communicating with the front opening of the cooling liquid pipe and with a back flow channel respectively formed between the shaft and the pipe.
A plunger of this kind is known from the DE-Patent 2 233 132. The known plunger is a multi-part structure. The front wall and the tube-like body are integrally formed. For communication between the annular chamber and the outlet opening of the cooling liquid pipe and the back flow channel respectively only small bores are provided one at the front end of the tube-like body and one at the rear end thereof. The liquid throughput and therefore the cooling effect are limited. Because of the small cross-section of the bores lime deposits will contract the small bores, additionally. The liquid flow is further obstructed and the danger exists that the cooling is completely interrupted with the result that at least the plunger can be destroyed.
From U.S. Pat. No. 4 334 575 a plunger is known which completely dispenses with a tube-like body for a controlled forced liquid flow. The cooling liquid pipe simply runs into the hollow plunger chamber. No doubt the danger of choking thereby is avoided but the cooling effect is remarkably reduced, because dead flow areas will exist and the cooling liquid leaving the feeding pipe can directly flow back into the back flow channel and the liquid at the front wall of the plunger remains substantially stationary and will not be exchanged.
Therefore it is one object of the invention to provide a plunger of the kind mentioned at the beginning comprising a tube-like body for producing a forced liquid flow in which plunger the heat transfer from the plunger to the cooling liquid is improved and the lifetime of the plunger is increased.
A further object of the invention is to provide a plunger which supplies a continuous liquid flow within the plunger exposing large areas of the plunger front wall to the cooling liquid.
One further object is to provide a plunger in which the tube-like body has a shape and is arranged such that flow obstructions of the cooling liquid are reduced to a minimum.
Last but not least it is one object of the invention to provide a novel plunger which completely avoids any choking of the flow channel system within the plunger.